Immunocompromised pediatric patients with HIV infection and other immunosuppressive disorders are susceptible to Pneumocystis carinii pneumonia. Bronchoscopy with bronchoalveolar lavage may be technically more difficult to perform in pediatric patients. Because of this, an alterative diagnostic method which was safe and reliable had to be determined. We have continued our prospective assessment of the utility of sputum induction for the diagnosis of P. carinii pneumonia in children. An ultrasonic nebulization technique using hypertonic sodium chloride with either expectoration, oropharyngeal or nasopharyngeal suctioning has been employed. Preliminary data indicate that P. carinii can be reliably diagnosed by this technique in children younger than one year. The technique is a very safe and effective alternative to bronchoscopy for children. Initial data from this study have appeared in the Journal of Pediatrics. The project is ongoing, and a major goal is to further improve the sampling technique in order to increase sensitivity. Diagnostic data subsequent to the initial manuscript are being collected and will be reviewed. The data will be analyzed in terms of technical improvements, diagnostic yield, sensitivity, specificity, and patient safety. The goals and significance of this project are to optimize the diagnostic sensitivity of this technique for P. carinii and to modify the technique as possible to limit patient morbidity. Of particular attention will be the impact of chemoprophylaxis (oral and aerosol) against P. carinii on the sensitivity of the technique. In addition, a special focus of this project is to identify the lowest age in which this procedure is possible, based on the technical modifications employed. This project has extended the clinical applicability of a diagnostic procedure, developed largely by NIH, which now offers many centers the option of a test that is less expensive, less invasive, and less associated with complications than bronchoscopy.